Having farmed Sand Devil and Shoguns Grove for the oils and dust multiple times I've come across the issue of how the rerolling of the stats works.

I have no issue using dusts to reroll the ascension stats however I believe that there should be some sort of bad luck protection.  It is theoretically possible (although unlikely) to reroll the ascension stats on gear and never get the one you are looking for.

Foe example, ascending gloves and getting a flat stat like HP.  You start using the dust to reroll the stats and get DEF flat stat first, then get HP again on the second reroll, DEF again on the third reroll and then ATK flat stat on the forth.  This goes on and on and you eventually use 22 rerolls and never get a stat reroll you can work with and while the cap of 9 dust helps it doesn't aid in how many rerolls are required to get what you want.

My suggestion is that ascension stats rerolls have some sort of bad luck protection.  Once a stat is rolled or rerolled it CANNOT reroll to stat it has already rolled either on the initial ascension or the rerolled ascension.  So for example in my previous example (which has actually happened to me) the stat cannot be HP on the second reroll from DEF and cannot be either DEF or HP on the next reroll etc.  This occurs until all stats have been rolled at least once before the stat can be rerolled.